1. Field of the Invention
The present invention relates to Hydroquinone di-(2-hydroxyethyl) ether, referred to as HQEE, which is widely used as a chain extender to make high performance polyurethane cast elastomers or thermoplastics elastomers in the polyurethane industry. The pure adduct of 2 moles of ethylene oxide (EO) and 1 mole of hydroquinone (HQ) is very crystalline and is believed to be desirable to get the best properties. However, for practical reasons, the pure adduct of 2 moles of EO and 1 mole of HQ is not available commercially. During ethoxylation of HQ with EO, due to kinetics, in addition to the desirable adduct, one also gets, mono adduct, triadducts, and higher adducts. In addition, the solvent used in the process also imparts impurities. Therefore, on a commercial scale, the HQEE grades available have 1–10% of non-desirable species and 99–90% of pure adduct (2 moles EO and 1 mole HQ). The impurities lower the final part properties and cause color instability for HQEE when HQEE is exposed to heat and/or oxygen. That is the color of HQEE goes up with time and temp. In many plants, HQEE is processed at elevated temp and there the color of HQEE goes up leading to parts, which are high in color. The color increase is very significant when light or pastel color parts are to be produced. Therefore, a practical method to stabilize the color of generally available grades of HQEE is desired and this invention provides such solution.
2. Brief Description of Art
It is well known that hydroquinone hydroxyethyl ethers (HQEE) are used for manufacturing of polyurethanes. Commercial grade hydroxyethyl ethers of hydroquinone contain >90% of hydroquinone bis(2-hyroxyethyl) ether. Due to the impurities contained in the product, they have tendency to discolor especially at higher temperatures. Hydroxyethyl ethers of hydroquinone are solids at room temperature and for application purposes are kept in molten condition. At increased temperature discoloration proceeds faster and there is a need for color stabilization to allow the use in color sensitive applications.
Color stabilization of hydroquinone hydroxyethyl ethers using phosphite type color stabilizer have been described in U.S. Pat. No. 3,592,858. According to the disclosure the phosphite molecule consists of either one or two cyclic phosphite groups attached to an aryl- or cycloalkyl ring. The result of color stabilization was not good enough to protect against discoloration for prolonged usage especially with commercial grades of hydroquinone hydroxyethyl ethers.